In order to optimize oil production from one or more oil wells, on-line measurement of at least the water content of the oil stream is required. Lighter oils can easily be separated from the water, and the oil can be assumed to be 100% oil and the water 100% water. However, these assumptions are not valid for heavier oils because the oil tends to emulsify in the water. So-called "test separators" therefore are used to separate the oil, water and any gas and measure the water content, for example using capacitance or RF admittance probes or conductivity measuring devices.
In traditional test separators, the full flow of the production stream flows through a test separator that includes a vessel in which the oil and water tend to separate. Gas is taken off from the top of the vessel and water from the bottom, while oil is removed from a level above the oil/water interface in the vessel. Individual measurements are taken of the flow of gas, water and oil to indicate the relative proportions of these components in the oil stream.
A large separator vessel is required and both the capital and operating costs of the equipment tend to be high. Also, in practice, the measurements derived from prior art test separators are subject to many errors.
An object of the present invention is to provide a method and apparatus for determining the water content of an oil stream that offers lower capital and operating costs and improved accuracy of measurement.